Method for producing magnetic materials



United. States Patent In the construction of static magnetic binary information storage devices, it has been found advantageous to employ rods or wires coated with magnetic material having a substantially rectangular magnetization curve, and

having a predetermined coercive force. Plates or layers of such materialmay also be employed for information storage; and the use of magnetic materials of rectangular magnetic characteristics is common for so-called magnetic amplifiers. The electrical arts in general make wide use of ferromagnetic materials of various magnetic, physical, and geometric properties. .Electrodeposition is a particularly convenient method of fabrication of metal parts, but its application to the production of magnetic cores for commercial purposes has not been commensurate with the use of electrodeposition in industry for other purposes. such as protective coatings; this reflects the difiiculty of controlling by the presently known art the magnetic properties, particularly the coercive force, of coatings thus deposited. While in some applications of magnetic matcrials, the coercive force does not matter providing it does not exceed some particular magnitude, in certain other uses, such as coincident current memories, it must be held between certain relatively close maximum and minimum values. My present invention specifies a method for electroplating iron-nickel alloysso as to produce closely controlled magnetic properties, particularly coercive force. (Coercive force will be specified in oersteds throughout this specification.)

The desirable range of coercive force of magnetic material, especially for information storage, is determined by the lower bound that it should exceed any expected stray fields by a sufficient amount that its operation will not be affected by the stray fields; and by the upper bound, that the coercive force required to switch it from one to another state of magnetization should not be so great that the power dissipated in it and the currents required to produce the requisite magnetomotive force gradient in it are inconveniently large. Obviously, the design of the particular equipment employing the magnetic material will itself determine some of the parameters which determine these bounds. In general, however, desirable coercive forces for many uses range from a few tenths of an oersted to fifty of a hundred oersteds.

The art of electroplating is, for one of the electrical arts, extremely old and, despite its relative antiquity, because it deals with materials, and particularly with materials in the solid form, and with the boundaries between different solid materials. tends to be very much an art. The parameters in electroplating are numerous and susceptible of wide variation. with interdependent effect.

The bath employed in the practice of my invention is a water solution of iron and nickel sulfamates. The parameters whose control is necessary or beneficial to obtain desired products are:

In producing materials of particularly low coercive force,"

annealing of the final product may be a necessary additional step, as will be further described.

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Thus one object of my invention is a method of plating nickel-iron alloys of closely predictable magnetic properties, particularly coercive force.

Another object of my invention is to provide a method of plating nickel-iron alloys of closely predictable magnetic properties from a bath less toxic and hazardous to operators than the baths commonly employed for plating purposes.

Other objects and benefits of my invention will appear in the course of the following specification.

The bath I employ in my invention is an aqueous solution of nickel sulfamate and iron sulfamate which is rendered acidic by the addition of sulfarnic acid. The magnetic coating whose production is an object of the process is deposited upon an electrode which is the cathode. The anode is preferably of soluble nickel or nickel-iron alloy. If the anode does not replace by its solution the material deposited from the bath on the cathode, corresponding salts must be added to the bath to maintain its composition at the desired values. Thus, the use of a pure nickel anode when nickel-iron alloy is being de' posited would require the addition to the bath of iron sulfamate to replenish the iron content. Operation such as described, where the depletion of the metallic content of the bath is not completely compensated by replenishment by anode solution will cause the pH of the bath to decrease. It may be adjusted upward by the addition of nickel carbonate which will also increase the nickel content of the bath, but not to an objectionable extent in the amounts required for pH adjustment. The products produced by my invention is the subject matter of a divisional application entitled Magnetic Materials, filed November 22, 1961, Serial No. 154,329.

In reducing this invention to a practical form, I have made numerous experiments, whose results are a part of the teaching of my invention. I therefore present in tabular form the results which I found for different concentrations of ionic iron, different concentrations of ionic nickel, different degrees of acidity or hydrogen-ion concentration (expressed in units of pH, conventional in the chemical and. electrochemical art), different bath temperatures, and different densities of plating current at the cathode. All depositions were one thousandth of an inch thick and were made on copper wire which had been stretched cold to a 5 percent increase in length (and thus presumably a 5 percent reduction in cross section) from an initial annealed state. The tables presented hereinafter are here listed for convenient reference.

Table 1.Coercive force of coating as deposited. coercive force of coating after annealing, and percent iron in the deposit, for a bath containing 25 grams per liter of iron as ferrous ion and 77 grams per liter of nickel as nickelous ion, for current densities from 0.17 to 5.0 amperes per square inch, for temperatures from to 195 degrees Fahrenheit, and a pH of 1.7.

Table 2.The same data as in Table l, for the same bath, the same current densities, and for temperatures from to degrees Fahrenheit, but for a pH of 2.5.

Table 3.Coercive force of coating as deposit d, coercive force of coating after annealing, and percent iron in the deposit, for a bath containing 49 grams per liter of iron as ferrous ion and 64 grams per liter of nickel as nickelous ion, for current densities from 0.17 to 5.0 amperes per square inch for temperatures from 70 to 195 degrees Fahrenheit, and a pH of 1.7.

Table 4.The same data as in Table 3, for the same bath, the same current densities, and for temperatures from 100 to 195 degrees Fahrenheit, but for a pH of 2.5.

Table 5.Coercivc force of coating as deposited, eo ercive force of coating after annealing, and percent iron in the deposit, for a bath containing 100 grams per liter of iron as ferrous ion and 39 grams per liter of nickel as nickelous ion, for current densities from 0.17 to 5.0 amperes per square inch, for temperatures from 70 degrees Fahrenheit to 195 degrees Fahrenheit, and a pH of 1.7.

Table 6.The same data as in Table 5, for the same bath, the same current densities, and for temperatures from 100 to 195 degrees Fahrenheit, but for a pH of 2.5.

Table 7.Coercive force of coating as deposited, coercive force of coating after annealing, and percent iron in the deposit, for a bath containing 149 grams per liter of iron as ferrous ion and 13 grams per liter of nickel as nickelous ion, for current densities from 0.17 to 5.0 amperes per square inch, for temperatures from 70 to 195 degrees Fahrenheit, and a pH of 1.7.

Table 8.The same data as in Table 7, for the same bath, the same current densities, and for temperatures from 100 to 195 degrees Fahrenheit, but for a pH of 2.5.

Table 9.Coercive force of coating as deposited, coercive force of coating after annealing, and percent iron in the deposit, for a bath containing 12 grams per liter of iron as ferrous ion and 39 grams per liter of nickel as nickelous ion, for current densities from 0.17 to 5 .0 am peres per square inch, for temperatures from 100 to 195 degrees Fahrenheit, and a pH of 1.7.

Table 10.The same data as in Table 9, for the same bath, the same current densities, and the same temperatures, but for a pH of 2.5.

Table lI.Coercive force of coating as deposited, coercive force of coating after annealing, and percent iron in the deposit, for a bath containing grams per liter of iron as ferrous ion and 32 grams per liter of nickel as nickelous ion, for current densities from 0.17 to 5.0 amperes per square inch, for temperatures from 100 to 195 degrees Fahrenheit, and a pH of 1.7.

Table 12.--Tl:1e same data as in Table 11, for the same bath, the same current densities, and the same temperatures, but for a pH of 2.5.

Table J3.Coercive force of coating as deposited, coercive force of coating after annealing, and percent iron in the deposit, for a bath containing 50 grams per liter of iron as ferrous ion and 20 grams per liter of nickel as nickelous ion, for current densities from 0.17 to 5 .0 amperes per square inch, for temperatures from 100 to 195 degrees Fahrenheit, and a pH of 1.7.

Table 14.The same data as in Table 13, for the same bath, the same current densities, and the same temperatures, but for a pH of 2.5.

Table 15.-Coercive force of coating as deposited, coercive force of coating after annealing, and percent iron in the deposit, for a bath containing 74 grams per liter of iron as ferrous ion and 6 grams per liter of nickel as nickelous ion, for current densities from 0.17 to 5.0 amperes per square inch, for temperatures from 100 to 195 degrees Fahrenheit, and a pH of 1.7.

Table 16.Tl1e same data as in Table 15, for the same bath, the same current densities, and the same temperatures, but for a pH of 2.5.

Key to tables: Since three different kinds of information are included in a single table, to avoid excessive repetition of captions the information is given according to a positional key. The coercive force before annealing is placed on a first line; the iron content is placed on the next line below, and to the right; and the coercive force after annealing is placed another line below, and still further to the right. Thus, for example, in Table 2, the first entries are:

Temperature Degrees F. Current density amps/sq. in.

This signifies that a current density of 0.17 ampere per square inch and a bath temperature of degrees Fahrenheit, a deposit was produced which had a coercive force before annealing of 13 oersteds, an iron content of 51 percent, and a coercive force after annealing of 7 oersteds. At the same current density, but at a temperature of degrees Fahrenheit, a deposit was produced with 3.7 oersteds coercive force before annealing, an iron content of 6.1 percent, and a coercive force after annealing of 6 oersleds. This presentation method is believed preferable to the presentation of three times the number of tables actually included herein.

TABLE 1 Bath: Iron 25 grams per liter, nickel 77 grams per liter, pH 1.7

. Temperature, degrees F. Current density amps/sq. in.

TABLE 2 Bath: Iron 25 grams per liter, nickel 77 grams per liter, pH 2.5

Temperature, degrees F. Current density amps/sq. in.

o as m 407 7 337 9 447 a 1.3 3.5 as

TABLE 3 Bath: Iron 49 grams per liter, nickel 64 grams per liter, pH 1.7

Current Temperature, degrees F. density ampsJaq. in.

TABLE 4 Bath: Iron 49 grams per liter, nickel 64 grams per liter, pH 2.5

Temperature, degrees F. Current density ampsJsq. in.

TABLE 5 Bath: Iran 100 grams per liter, nickel 39 grams per liter, pH 1.7

Temperature, degrees F. Current density amps./sq. in.

TABLE 5-Cor1tinued Temperlture, degrees F.

Current density ampsJsq. in.

TABLE 6 Bath: Iron 100 grams per liter, nickel 39 grams per liter, pH 2.5

Temperature degrees F. Current density ampaJsq. in.

TABLE 7 Bath: Iron 149 grams per liter, nickel 13 grams per liter, pH 1.7

Temperature, degrees F. Current density ampsJsq. in.

7 TABLE 8 Bath: Iron 149 grams per liter, nickel 13 grams per liter, pH 2.6

Temperature, degrees F.

Current density ampsJsq. in.

TABLE 9 Bath: Iron 12 grams per liter, nickel 39 grams per liter, pH 1.7

Temperature, degrees F. Current, denisity amps. sq. n. 100 150 195 3a TABLE 10 Beth: Iron 12 gram per liter, nickel 39 grams per liter, pH 2.5

Temperature, degrees F. Current density ampsJsq. in.

Bath: Iron 25 grams per liter, nickel 32 grams per liter, pH 1.7

Temperature, degrees F. Current density empsJsq. in.

TABLE 12 Bath: Iron 25 grams per liter, nickel 32 grams per liter, pH 2.5

Tem ature degrees F. Current denigity W amps. sq.

TABLE 13 Bath: Iron 50 grams per liter, nickel 20 grams per liter, pH 1.7

Temperature, degrees F. Current density amps/sq. in.

TABLE 14 Bath: Iron 50 grams per liter, nickel 20 grams per liter, pH 2.5

Current density Temperature, degrees F.

Bath: Iron 74 grams per liter, nickel 6 grams per liter, pH 1.7

Temperature, degrees F.

Current density am s.s .1n.

p lq 100 150 195 TABLE 15-Continued Temperature, degrees F. Current, denislty am s. s n.

TABLE 16 Bath: Iron 74 grams per liter, nickel 6 grams per liter, pH 2.5

Temperature, degrees F. Current, denisity amps. sq. n.

3.5 a e a 6.5

Reference to Tables 1 through 16, inclusive, reveals that a large range of values of coercive force may be obtained by varying the parameters of the plating operation. Specifically, values from less than one oersted to over one hundred oersteds are obtainable. Although annealing is generally expected according to the art to produce a reduction in coercive force, annealing unexpectedly produced an increase in approximately as many cases as it produced a decrease in coercive force. The annealing process employed in the practice of my invention, where annealing is a step in obtaining the desired properties may consist of heating for three hours at 300 degrees centigrade in hydrogen. This is not critical; the time and the temperature are adequate to produce the desired effect, and the hydrogen is a preventive of oxidation of the metal deposit. Other, moredrastic' annealing treatments may be found desirable for certain materials and applications. One trend which appears, from a study of the data, is that a temperature of 150 degrees Fahrenheit and a pH of 1.7 is favorable to the production of a low coercive force in the annealed material, particularly for a middle range of current densities listed. As a specific example, Table 3 for current density of 2.5 amperes per square inch and a temperature of 150 degrees Fahrenheit, 49 grams per liter of ferrous ion and 64 grams per liter of nickelousion, at a pH of 1.7 shows a coercive force after annealing of 0.1 oersted. This is one preferred mode of operation of my invention, to obtain low coercive force material after annealing.

Table 3 indicates that for current density of 1.67 amperes per square inch and a temperature of 195 degrees Fahrenheit, 49 grams per liter of ferrous ion and 64 grams per liter of nickelous ion, at a pH of 1.7 a deposit is obtained whose coercive force before annealing is 125 oersteds. This is a mode of operation suitable for producing relatively high coercive force; and the required conditions differ surprisingly little from those for low coercive force.

However, since the problem of controlling the parameters of a plating operation is sometimes burdensome, especially in large scale production operations, it is desirable to select an operating point such that small departures from the selected values of parameters will not produce a very great change in the result obtained. Thus reference to Table 18 indicates that for a current density of 1.67 amperes per square inch, a temperature of 150 degrees Fahrenheit, 5 grams per liter of ferrous ion and 77 grams per liter of nickelous ion, at a pH of 2.5, a deposit will be obtained with a coercive force of the order of 100 oersteds, and small changes in current density will have only slight influence on the result.

I have found in the course of my tests that a practical upper limit for the pHof nickel and iron sulfamate plating baths is pH equal to 4, since a higher pH value tends to permit precipitation of hydroxides of iron, which is undesirable both because it arbitrarily changes the bath composition, and produces a mechanical contaminant in the bath. While I conducted the tests whose results are included in the tables at a minimum pH of 1.7, I have found that it is possible to employ lower values of pH, but for this purpose it is necessary to increase the current density to obtain an equivalent result. Thus it appears that for the most convenient and best operation of my invention, a value of pH not less than 1.5 nor more that 4 is preferable. Similarly, a temperature range between usual room temperature and the boiling point of the bath is preferable.

l have also found in the course of my tests that iron tends to be deposited more readily from the nickel and iron sulfamade bath than does nickel. Thus apparently the layer of electrolyte next the cathode tends to become depleted of iron first, especially if the concentration of iron is small relative to that of nickel. To keep the percentage of iron in the deposit constant with an increase in current density, it is necessary to increase the concentration of iron in the bath. An increase in bath temperature, presumably by increasing the rate of diffusion of iron from the remoter parts of the bath toward the depleted layer next the cathode, has an elfect similar to that of increasing the iron concentration.

The correlation between the composition of the deposit 12 and its magnetic properties is very vague at best; this is assumed to be due to the known large effect of internal stresses upon the magnetic properties. Thus the magnetic properties are not predictable by the application of any art which might propose to predict composition of the deposit.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced other than as specifically described and illustrated.

What is claimed is:

1. The process comprising electrodepositing a magnetic nickel-iron alloy having a coercive force of not more than 10 oersteds from an aqueous bath whose content of metallic cations consists of between 5 and 150 grams per liter of iron as dissolved iron sulfamate and between 6 and 77 grams per liter of nickel as dissolved nickel sulfamate, having a pH between 1.5 and 4.0, at a temperature between and 200 degrees Fahrenheit, upon a cathode operating at a current density between 0.17 amfiere per square inch and 10.0 amperes per square inc 2. The process comprising electrodepositing a magnetic nickel-iron alloy having a coercive force of not more than 10 oersteds from an aqueous bath whose content of cations of metals electrodepositable from aqueous solution consists of between 5 and grams per liter of iron as dissolved iron sulfamate and between 6 and 77 grams per liter of nickel as dissolved nickel sulfamate, having a pH between 1.5 and 4.0, at a temperature between 70 and 200 degrees Fahrenheit, upon a cathode operating at a current density between 0.17 ampere per square inch and 10.0 amperes per square inch.

3. The process as defined in claim 1 including the step of annealing the magnetic nickel-iron alloy thus produced.

4. The process as defined in claim 2 including the step of annealing the magnetic nickel-iron alloy thus produced.

References Cited in the file of this patent UNITED STATES PATENTS 2,443,756 Williams et al. June 22, 1948 2,726,179 Ortlieb et al. Dec. 6, 1955 2,808,345 Traub Oct. 1, 1957 2,840,517 Faust et al. June 24, 1958 OTHER REFERENCES Haynes: Elements of Magnetic Tape Recording, Prentice Hall Inc. (1957), page 38. 

1. THE PROCESS COMPRISING ELECTRODEPOSITING A MAGNETIC NICKEL-IRON ALLOY HAVING A COERCIVE FORCE OF NOT MORE THAN 10 OERSTEDS FROM AN AQUEOUS BATH WHOSE CONTENT OF METALLIC CATIONS CONSISTS OF BETWEEN 5 AND 150 GRAMS PER LITER OF IRON AS DISSOLVED IRON SULFAMATE AND BETWEEN 6 AND 77 GRAMS PER LITER OF NICKEL AS DISSOLVED NICKEL SULFAMATE, HAVING A PH BETWEEN 1.5 AND 4.0, AT A TEMPERATURE BETWEEN 70 AND 200 DEGREES FAHRENHEIT, UPON A CATHODE OPERATING AT A CURRENT DENSITY BETWEEN 0.17 AMPERE PER SQUARE INCH AND 10.0 AMPERES PER SQUARE INCH. 